Massive MIMO: Key to Simplified 5G Networks

13 MAR 2019

2019 will see the world’s first 5G commercial deployments in some markets. Whether 5G networks can be constructed economically is a focus of global operators. One of the common expectations of 5G is the Gbps-level experience it will bring. But how can we make such an ultimate experience a reality? If 5G is deployed in high-frequency bands such as C-Band (3.5 GHz), does that mean a dense network, which calls for more new sites and greater costs? Or is a low-band 5G network, especially in bands below 2 GHz, a better option, which delivers similar coverage as LTE and costs less?

At the debate session on “5G Deployments in High-Frequency Bands are Uneconomic” on February 26 at the Mobile World Conference (MWC) 2019, Mr. Yang Chaobin, president of Huawei’s 5G product line, elaborated on the idea that Massive Multiple-Input Multiple-Output (Massive MIMO) is the key to simplified 5G networks. Drawing on rigorous theoretical analysis and extensive testing results, he responded positively to the much debated topic on the economy of 5G network construction. Deployed on the same sites with LTE in 1:1 mode, Mr. Yang emphasized, 5G with 3.5 GHz Massive MIMO delivers better coverage and greater capacity than LTE. In addition, operators will see significantly lower cost per bit and lower overall deployment costs.

The Massive MIMO gains can compensate for the extra free space path loss due to high frequency calculated from the Friis transmission formula.

The Friis transmission formula is one of the most important formulae in the antenna theory. It calculates the received power of a radio wave from a transmit antenna given a transmission frequency. In other words, it denotes the free space path loss for different frequencies. The higher the frequency, the less the received power, the greater the path loss. Specifically, radio waves on 3.5 GHz experience about 6 dB more free space path loss than on 1.8 GHz.

The core of Massive MIMO is the large-scale antenna arrays. The traditional 1.8 GHz antenna array consists of 24 antenna elements, while the Massive MIMO antenna array has as many as several hundred antenna elements. Admittedly, while the number of antenna elements rises, each antenna element delivers smaller gains. Yet even so, the beamforming gains brought by the Massive MIMO antenna array can compensate for the extra 6 dB loss on 3.5 GHz. Therefore, 3.5 GHz 64T64R delivers better coverage than 1.8 GHz, 3.5 GHz 32T32R the same coverage, while 3.5 GHz 16T16R/8T8R worse coverage.

Massive MIMO and the Shannon theorem enable the capacity of 5G to be nearly 100 times that of LTE.

The Shannon theorem tells how the channel bandwidth and signal-to-noise ratio (SNR) influence the theoretical maximum channel capacity. 5G capacity is greater in nature thanks to the 100 MHz large bandwidth and Polar code, an advanced coding scheme that improves the SNR. However, spectrum resources are limited and the Polar code is about to run out. With these restrictions, how can we further improve channel capacity? Massive MIMO is the answer. It uses an increased number of antenna arrays to enhance the capability of spatial multiplexing, which in turn improves channel capacity.

The field test in Beijing organized by the IMT-2020 (5G) Promotion Group has just witnessed a new record of 5G cell capacity: With 3.5 GHz 64T64R Massive MIMO and the 100 MHz bandwidth, 5G cell capacity reaches 14.58 Gbps, which is 97 times as great as that of LTE theoretical throughput 150Mbps. In addition, Massive MIMO significantly reduces the cost per bit.

The antenna array of smaller size for high frequency facilitates the engineering of Massive MIMO.

The antenna size is an important factor that affects the engineering efficiency and determines the construction costs of base stations. It is closely related to the size of antenna arrays, which depend on the frequency (Frequency = Speed of light/Wavelength). Generally, the size of a single antenna element and the spacing between antenna elements are half the wavelength. Since higher frequency means shorter wavelength, the antenna array for high-frequency Massive MIMO is smaller. The antenna array of 3.5GHz 64T64R Massive MIMO is about 700×400 mm, while the antenna arrays of 1.8 GHz and 800MHz 64T64R are 1000×650 mm and 2000×1500 mm, respectively. Therefore, the 3.5 GHz Massive MIMO antenna is smaller and more feasible in engineering.

3.5 GHz Massive MIMO has been deployed on more than 10,000 sites in the large-scale 5G commercial network in Korea. Thanks to the small size and light weight of Massive MIMO antennas, all these 5G sites were finished within four months. A Massive MIMO module integrates a radio frequency (RF) unit and an antenna, so feeders are not necessary. Compared with the traditional RF module+feeder+antenna site form, the new-generation module reduces the size by 55% and takes 35% less installation time. This greatly improves the 5G deployment efficiency and helps the operator secure a leading position in 5G commercial deployment.